1. Field of the Invention
The present invention relates to damage control materials for warship construction and, more particularly, to a warship construction including an energy absorbing composition positioned to surround and protect areas of the ship that house critical elements and personnel required to accomplish the ship's mission. More particularly, the present invention relates to such a warship wherein the energy absorbing composition includes hollow microspheres and hollow macrospheres in a resin matrix.
2. Description of Prior Art
Warships are constructed from metal plates designed to withstand impact explosion and shock forces of weapons which are designed to damage or sink the ship. While the plates and the supporting structure for the plates, such as web frames or girders, improve the defense strength of the ship, limitations on their size are imposed, primarily due to considerations of ship buoyancy, ship stability and ease of ship handling during passage on the sea. Ships are formed of hulls having a variety of configurations. Some ships have double bottoms and double sides to form an inner hull and an outer hull, traditionally termed a double hull construction. In large ships, the space between the two hulls typically is at least about two meters. The volume defined by the inner surface of the inner hull comprises the volume within which the ships personnel are housed and within which weapons and supplies, including munitions are stored. The double hull design conventionally is orthogonally-stiffened by both transverse web frames and longitudinal girder (or longitudinal "webs") between the inner and outer hulls to form a stiff grid bottom structure beneath the main volume of the ship. While it is known that double hulls can effectively protect against minor impact forces, it is also known that they are ineffective to withstand strong impact forces such as that derived from weapons effects directed at the ship. Such strong impact forces cause both the inner and outer hulls to be breached. Areas of the warship, in addition to the hull, also must be protected against impact forces from incoming projectiles directed at the ship during times of war. Additional protection in specific areas of the ship may be required for the isolation of damage due to weapons effects or other extremely high energy releasing events. These areas include housing of personnel, munitions, offensive weapons and the ship's communication system.
It has been proposed to provide strength enhancing and shock absorbing elements between the two hulls of double hull ship. It also has been proposed to provide a foam material between the two hull to provide improved hull strength. Such arrangements are shown, for example in U.S. Pat. Nos. 3,811,141; 3,831,212; 3,840,296; 3,887,952 and 3,911,190. It has also been proposed to utilized hollow beads between the two hulls, as for example by U.S. Pat. No. 3,124,626. While the use of foam material or hollow beads comprise an improvement over a hollow space between the two hulls to effect absorbance and diffusion of force applied to the outer hull and to reduce force transmission to the inner hull, their use is undesirable since a significant portion of the impact force is transmitted to the inner hull.
It has also been proposed in U.S. Pat. No. 5,353,727 to provide a collision guard to the exterior hull surface of a marine vessel which is formed from a lightweight permanent buoyant material, such as a fire retardant foam, in order to improve resistance against forces applied to the exterior hull. Such modules are undesirable since they are subjected to the normal sea forces to which a vessel is subjected resulting in their detachment from the vessel.
It has been proposed in U.S. Pat. No. 5,277,145 to increase the strength of a transom portion of a boat with syntactic foam formed from a resin containing hollow microspheres, usually made of glass. These microspheres generally have a diameter of between about 1 and about 100 microns. Such syntactic foam compositions are undesirable for use between hulls of double hull since they preferentially transmit rather than absorb forces applied to them. This is primarily due to the fact that the microspheres, when embedded within a thermosetting resin, are extremely resistant to impact forces and thus transmit impact force through the composition rather than collapsing up to the point wherein very high impact forces are applied to the syntactic foams.
Modified syntactic foam are disclosed in U.S. Pat. No. 3,622,437 for use as buoyant materials to be positioned in sea environments, for example more than a thousand feet below the surface of the sea. Such modified syntactic foams include relatively large hollow spheres which provide a reduced density for the modified syntactic foam as compared to the unmodified syntactic foam.
Accordingly, it would be desirable to provide a warship construction which includes an energy absorbing composition positioned in those areas of the warship requiring protection. In addition, it would be desirable to provide such a composition which does not significantly adversely effect the buoyancy of the vessel when the composition is positioned within the warship. Furthermore, it would be desirable to provide such a composition which preferentially absorbs energy when excessive energy is applied to it rather than transmitting energy to the ship's structural elements so that critical areas of the ship remain protected.